Telegraph switching system



April 20, 1954 W, M, BACON TELEGRAPH SWITCHING SYSTEM Filed Dec. 29, 1949 4 Sheets-Sheet 1 April 20, 1954 w. M. BACON 2,676,199

TELEGRAPH SWITCHING SYSTEM vit Sheets-Sheet 2 Filed Dec. 29, 1949 im /Nl/ENmQ 5E WM. BACON im* d V cro V F/c. 2

April 20, 1954 W, M, BACON 2,676,199

TELEGRAPH SWITCHING SYSTEM Filed Dec. 29, 1949 4 Sheets-Sheet 3 S lu 8 u -1 /NVENTOR By WM BACON A TTORNEV April 20, 1954 w. M. BACON 2,676,199

TELEGRAPH SWITCHING SYSTEMl Filed Deo. 29, 1949 4 Sheets-Sheet 4 LOOP /2 LOOP /Nl/ETOR y WM. BACON B KTQ? LEVEL /i LEVELS LEVEL 6 Patented Apr. 20, 1954 TENT OFFLICE 2,676,199 "TELEGRAP'H SWITCEIG "SYSTEM 4Falter 'll/I. Bacon-New York,'N. Y., assignor to rBelllelephone-Iiaboratories,llncorpcrateri, :New York,- N. i, -a corporation Aof New York rpplicationieeerber 29, 1949, Serial nlm-135,811

(C1. ITI-8&2)

15 Glaims.

No. 1,904,164 to Sterling Morton et granted `April 113,1?1933em15loy's1at the transmitting end, a jTperf'ora-tin'g machine l-vi'h'ich translates .the 'let- 'ters Lorfsynibo'ls rt'olla'e transmitted to peiforatiens infa `paper tape. f'Start-stop transmitters are in turn `'operated by -Ineans 'of this perforated ta'p'e, transforming the 'code combinations ef peri-inra tions "in the tape linto groups of electrical irnpulses. "These impulses 'are Atrans'rnitted -via a transmission line lto a receiving 4location, -and are interpreted, and thele'tt'ers--or symbolsrepresented by the received `impulses Yare thereupon caused to be printed.

`1t isoften desirable to retransmittne incoming signals arriving at a'receivings'tation 'to-a particular desired vlocation remote "from the ren "ceiving station. 'Itisa particular object or" Athe invention lto 'provide vmeans'o' forwarding such received signalsto any `one of agroupnf 'remotely locate'd'sub-re'ceiving Astationsto 'Whichthe niessage @is ultimately to be transmitted. in surnmary, the invention Will `provide means of 'starting and stopping retransmitting `equipment "lou cated at "thecentr'al receiving stationat :the beginriing and end respectively of each message; vWill 'forward a message to 'a chosen sun-reeei'w ing-position when 'the particular line lassociated with the-'subweceiving station is 'free anni 'will store'suchf-inessage'inthe-event the line is 'busy until Vsu'eh time as it shall become free.

This -'s`peci`catin Will -describ'e 'the f central receiving station and the accompanying Aretransmission 4Mequipment to'disp'erseithe received inteliligence yto rthe aforesaid remotely llocated subreceiying stations. "However, the general operation'of the origin'altransmission station'and `the character ofthe signals transmitted `should loe understood for a complete understanding of vthe 'nveritin entrare-stopautomatictaegraphsystems, 'the i2 transmitters "are customarily operated by iper- Vfcrated ta'pe. vAt -the 'source of lthe yliesired fintelleig'ence, an operator causes -the Itape ff o lo'e 'perforated in -groups -ofperforationswhiehfrepresent theletters or ysymbols to betransmitted. 2A sensing arrangement lis provided which :determines =the number and arrangement ici "tli'ep'erorations uIrepresenting a ffgiven letter lor symb'ol, and the information thus 'desired isfsuppli'ed to awlistributor system :in fthe transmitter. This transmitter samples eac'hifof "theiaforemention'ed sensingl `pins 'to determinefwhetheror `=not it senses a perforation. The intelligence found :oni-the reia'tive sensing `pins @is analyzed 7'Joy the distributor with respect to time and in addition, the vdistrimiter ordinarily passes a sensing position which vis -used 'to synchronize a reeeiver remotely located. 'This system is lvvell knownfandfdescribed in UnitedStates Patent No. 11,566,295 't'o Watson granted etober '-1-7, 1922. vIn `-lorief, th'e Adesired `intelligence is caused vto -be transmitted "in the ferm for ielectrical impulses -over a itr'an'srni' ion lin'eftoffa receiver which Acan analyze the pulses and `print "the 'originally transmitted intelligerff'e in a'known manner.

electrical impulses Aheretofore '-mentine'l 'a'rek'nfowniin thes'art'of telegraphyibythe 't s marking and spacing These 'werds identify-tw() A'contraStingicOndt'fJnS-'fthe yline. Thus, in 'certain telegraphic systems, means Fare ipr'ov-ic'e'd 'for causing current 'to lflow in fthe *line for for preventing the nov/sof current in VVtine ilineat the 'tr-ansmi'tter. `In such a' system, therr` line may bef said to yhe -in fa `marking condition when Vfour-- rent is flowing and -a spacing condition 'current 'is not owing. It will be understood that inother'types of systems, the 'terms marking and vspacing may have slightly Afcliierent meanings, as in telegr'aphi'c systems 'f 'the polarized type, in which two l contrasting conditions 1to which the Areceiver lis responsive, VEare 'the vff current in Jthe li'rst direction 'a flow fo rent in the reverse direction. The 'tei-ms niark- `ing`a`11d Spacing`hthe latter-'case will m to thedretdn 0f theIOW*Oficulrent'thertlfin theexistence or absence of current.

The Various incoming llines to thenen'tral receiving station will be referred'toasftheyarious incoming levels, "as `distinguished A'from the various outgoing "lines yto the Vren'lotely Llo" ':ated sub-receiving stations, which yllltb'e ealled'th'e outgoing loops. y

The invention is lmore fully vdescribenin the following specicatio'n: Fig. 1 shows ha sinip'liii'ei' bleek 'diagram to assist in explaining a system according to the invention;

Figs. 2, 3 and 4 show a preferred embodiment of the invention, indicating the schematic circuits employed at the central receiving stations; and

Fig. 5 shows the interrelation of Figs. 2, 3 and 4.

lReferring now tc Fig. l, the simplified diagram of the system according to the invention, it is to be noted that a number of incoming levels lili are provided. Each of these incoming levels may have intelligence thereupon in the form of marking and spacing conditions. Each of the incoming intelligences are supplied to the reperfcrator i532 which produces a perforated tape 63. This tape has perfcraticns which depend in number and arrangement along any given line normal tc the direction of tape motion representative of the letters or symbols forming the desired intelligence, much in the manner of the original transmitting operation hereinbeore described. Such a reperforator is shown in United States Patent No. 2,255,794 to R. A. Lake, granted September 16, 1949. This reperforator operates as described and in addition, will simultaneously provide a printed interpretation of the perforations made. rI'his will be later shown useful in determining the sub-receiving position addressed. While three incoming levels are shown, it is within the scope ci the invention to provide any number of incoming levels.

rEhe tapes supplied from the reperforators are delivered to the respective transmitters lila. Each of the transmitters Hl interprets the periorations made by the associated reperorator to provide groups of electrical marking and spacing pulses representative of the intelligence to be transmitted. Any number of outgoing loops ille extend from the central receiving station shown generally in Fig. l to remotely located receiving stations, not shown. When a predetermined code symbol is sensed by one of the transmitters, this code symbol activates the associated message start circuit ist. The message start circuit causes the associated lamp L ll to light and indicate to the operator at the central receiving position that a message is being received for retransmission to one of the remotely located sub-receiving stations. Further, the associated central receiving station transmitter 104 stops, and the tape containing the received message accumulates. The operator will then determine, by an inspection or" the tape or other means, to which of the remote sub-receiving stations the message is to be forwarded.

Each of the outgoing loops 95 to the sub-receiving stations has associated therewith a socalled preempt and "seizing circuit for each of the incoming levels; thus, for twelve outgoing loops representing twelve remotely located subreceiving stations and three incoming levels, thirty-six preempting and seizing circuits must be provided. For example, the upper incoming level and furthest left-hand outgoing loop will be associated in common with preempt circuit l and seize circuit H59. The apparatus of the preempting and seizing circuits will be later described.

When the operator has determined which of the sub-receiving stations is tc receive the message as previously indicated, it will be necessary to operate a key shown as K associated with the preempt circuit common to the incoming level through which the message is being received and the outgoing loop associated with the particular sub-receiving station to which the mes'- sage is addressed. Thus, to attempt connection between the upper incoming level and left-hand outgoing loop, the key H0 must be operated. Operation of the appropriate' key K will at once extinguish the lamp, indicating that a message is waiting, and will connect the appropriate incoming level tc the appropriate outgoing loop through the seizing circuit and the ring circuit, later to be described, if the outgoing loop is at that time free.

Operation of the K key will produce a preparatory condition in the various circuits of the invention; the stepping pulse circuit ill will be set into operation. The stepping pulse circuit drives a group of relays to be found in the various blocks marked ring l l2. The function of the ring relays is tc citer a connection of each of the receiving levels to the seize relay associated with a K key previously operated. If the outgoing loop associated with the operated K" key is at that time busy, the stepping pulse arrangement will continue in operation and the ring relays will offer connections between each of the Various levels ci incoming lines to all the outgoing loops in rapid succession. As long as any K key has established a preparatory condition which remains unsatised, e. g., because of a busy circuit, the stepping pulses will continue and the relay rings will also continue to offer connections as stated. When all the waiting incoming levels have been satisfied and have been connected to the appropriate outgoing loops. the stepping pulse circuit and the ring of relays will stop until another preparatory condition is established.

When an operating condition is achieved, that is, when the desired intelligence is supplied from the incoming level to the appropriate outgoing line through the seize relay, the seize circuit will start the transmitter in operation which in turn causes the accumulating tape to be fed to the transmitter; the message will be retransmitted to the remote sub-receiving location. There follows a more detailed description4 of a preferred embodiment of the invention.

Reperfomtor and transmitter The incoming intelligence received on the various incoming levels is received by a reperorator, as previously indicated. Referring now to Fig. 2, only one incoming level is shown in detail. This level is supplied with a reperforator i2, which produces a message tape il. The tape is in turn delivered to a transmitter 8l, shown in the dotted enclosure. rThe reperforator and transmitter form the first of the circuits providing for the retransmission of the signals to the appropriate remotely located sub-receiving station.

Tape transmitters are heretofore known. Such tape transmitters receive perforated tape, which in this instance has been prepared by the reperforator, and depending upon the positions of combinations cf perforated and unperiorated areas in the tape, the tape transmitter will transmit to its line output various code combinations. The code combinations normally include a start pulse, which may be a spacing pulse, and live code pulses which may be various combinations of marking or spacing pulses depending cn the perforations of the tape, and a stop pulse which may be a marking pulse.

As shown in Fig. 2, the tape transmitterl in. cludes a distributor having a solid inner distribu'ti'ng rlin'g I6 and ya lfsegme'rited outer distributing ring, Eboth 'of which are suitably:attachedfto the upper surface or" an insulating disc, Lnot show-n. 4The 'outer .distributing ring r`'is divided into seven segments insulated one from another, which include 'a stop segment, ais-tart segment, and'iive code pulse segments numbered -l 'through 5 inthe drawing. The distributor 'brush arm l continuously engages the'inneriring it and'successively engages segments of the outer 'ring with a wipingmovement. `"Connected tothe respective segments l throughlE are a group oft've contact armatures 'such ast. There are provided flve'lower contacts such v'as S and've-'upperff'contacts 'such as it vfor each of the kcontacttarmatures such as e. In order to sense the 'perforations inthe tape l'fl, Which is 4fedt'o 'thetransmitter from the reperiorator @there are provided vfive "Sensing pins, one r"foreach of ithe contact armatures as t, and mechanicalflinkages extend from each sensing pinto lits yassociated contact armature "for 'controlling the armature position. Sensing pins and contact larmaturesof the -type described are ullydisclosedin United States vPatent No. 2,055,057 to E Watson, granted September '29, 1936, to which reference is made for more complete detail. The contact armatures such as 8 yin Fig. 2 of the-present application may be considered to Yrepresent 'schematically the entire means for 'sensing'the perorations of the tape and lwinch make contact between "the`various leads to the respective contact armatures `as 8 and upper orlower contact sets as 9 and vlll in responseto the code'perfora'- tions.

The arrangement is such that When a 4sensing pin engages a hole in the tape, the armature, for example '8, controlled by its associated sensing pin engages the appropriate upper contact l0. This wllbe shown to provide a marking condition in the lead running from the armature sensing a perforation. The tape il is provided with a series of feed holes arranged approximately along the center line of the tape by which it is intermittently advanced through a mechanism linked tothe distributor shaft i3. The distributor brush arm l is carried by shaft i3 which is in turndriven by a motor through rictionclutch I4 and Worm gear drive l5. `'The motor is supplied with current from a source it through a manually operable control vswitch il.

1 Synchronization is achieved between the central receiving vstation transmitter and the associated start-stop sub-receiving station'receiver by impulses transmitted from the vstop and start segi ments of the outer ring oi the distributor shown in 87. The stop segment ci 'the outer ring of the distributor is connected to ground'and the start segment is connected to a 'battery 2'2-a providing, in this case, the necessary electrical impulses.

In normal operation ofthe transmitter, Ja'difference .may freduentiy occur between the rate at which 'th'e'transmitter operates 'and that iat which the tape il may be supplied fromthereperforator i2 to the transmitter Sl. .As has fp'reviously been indicated, various control circuits according to the invention may 'cause .one or more of the transmitters to stop entirely until certain functions have been performed. -Whenthis occurs, the reperforator associated with thestopped transmitterwill ordinarily maintain-its tape voutput' and the tape will be stored between the reperforator and the transmitter until vthe transmitter-is again started. It may-also he, seen that 6V when vthe reper'foratari operation ris interrupted or stopped at the end of a messagatthe transmitter may ultimately use up all the slack vin'lthe'tape and proceed'y to damagethe tapefeed'holes unless provision Were made 'to stop the *transmitter automatically.

To understand the means'fortaking careo'ff the difference between 'the rates ofoperation-oftl'ie transmitter vand the reperforator, the general'op'- eration 'of the distributor shaft :system 'must-be understood. There is 'iixedly mounted -on 'the main drive shaft i3, a stop cam "l'fformed with a peripheral shoulder IB-a. Associated Wi-ththe stop cam is alpi-voted stop-arm t9. vOne end'f the arm litis urged to engage the periphery-:df thestopoam 'by aspring 23. Theoppos'ite'en ofthe stop-'arm fi 9 is 'magnetically associatedwith an electromagnet 2i known '-a's the"startl=magnet. Electromagnet '.2 irisV employed to move the stop arm I9 about Vits pivot, that kit maybemoved out of engagement Withthe stop-cam periphery When-the distributoristo rotate. Electromagnet 2i vis connected electricallyin-series withaf battery 22, with the made contact of relay '23, through the contacts of .a stop lever .24, and thence through the made yleft-hand contactof relay 25 to ground and to theright-hand Contact of relay 26. Relay 23 and stop arm .24 are adapted to open --the series circuit/to '.thestart magnet 2i independently,.and-eitherrelayi or 2t mayopen the series circuit ntradependently. The winding of relay .2.3 :is in series with the battory, with tape-outsto p arm-21 and its associated contact 2li-a, .and with a .slack'tape arm and its associated contact t28-a, tex-"ground, When there .is -a normal amount .of slack etape H, .the slack tape arm 2B engages the contact .2t-a. When a taut tape condition-exists, contact 2S-a and `arm :23 `will be opened, releasing the start magnet 2i 'and .stopping the'distributor from its rotation. If thereperforator should runout of tape, tape-out stop 21 will break with its associated contact Z'l-"a, releasing the start magnet-2i and stopping the transmitter.

`Before the vtape transmitter is turned on for transmitting messages, both lthe manually operable motor `switch il and .the nlanuallyfoperabie transmitter'stop :switch 2d must be closed. in starting up --the transmitter, vthe vswitch "El 4--is rst closed :and the :motor will rotate` IArm la Willpreventrotation ofthe distributor shaft i3; and thefrictionfclutch is allows rotation oi .the motor shaft despite 'the fact that the shaft i3 and'fworm drive le arezstationary. Whenfasethe next step, :the marmally operable switch .2d is closed, `current from the battery 22 energizes the startfmagnetl which attracts the right-hand end 'of :arm I9, 'causing :this Vvarrn to 'pivot in :a counter-'clockwise `direction, V.thereby releasing the stop camflt. The distributor will then rotate. At any timethat'the startmagnet 2l is deenergized, fthe arm i9 engages the shoulder it-n, preventing the 'rotation 'of 'the distributor. 'ln thelatter case, the motorimaystill continue to rotate because it is coupled'to the transmitter through the friction clutch le.

A'tape feed withhold magnet 2S is sofcoup-led to the tape feed mechanism 'that its 'operation will prevent 4the feeding of tape to the'transmittel' 4although the/distributor shaft is rotating. Suche. tape -feed withhold magnet arrangement is vshown in Uni-ted -State-s yPatent No.

2,381,871, granted. August f1.4, i945 to .myself others. "Withheld magnet de `-is Vin 'iseries with 7 the battery 22 and the open, outer right-hand contact of relay 30.

Distributor shaft i3 has an additional cam 3| which rotates with it. Upon each rotation of the distributor shaft, engaged with arm i9, a shoulder of cam 3| closes auxiliary contact 33 with armature 32. Auxiliary contact armature 32 is connected to ground and makes to its associated contact 33 and thence to the made right-hand armature and contact of relay 25, shown in operated position, and to the left-hand armatures of relays 3!! and 35.

Referring to Fig. 3, blocks Sil-a and 39-0 represent circuits as shown in Fig. 2 for two diverse incoming levels. Blocks 35i-b and 39-d represent relays and circuits, similar to those shown in Fig. 3 on the left-hand side of the dotted division, for these two incoming levels.

Starting of message It has been stated that a predetermined letter or symbol sent in the form of intelligence over the incoming line will activate the operation of the circuit according to the invention. It may be assumed that some printing telegraph code signal such as the code signal indicating the presentation of the printing mechanism in the lower case condition may be the signal utilized as a starting point for the message. One standard printing telegraph code utilizes five perforations, one for each of the sensing pins, to indicate this lower case symbol and is known in the art as the Letters symbol. The perforation code for Letters may be indicated by the code group MMMMM where M is equivalent to a marking condition on the line. Relay 3S is a balanced polarized relay. When the system is in normal operation, relay 25 will be operated as shown; the winding of relay 25 is connected in series with battery and to the closed left-hand contact and armature of relay 31 to ground. In turn, the upper winding of relay 35 is connected in series with the made right-hand armature and contact of relay 25 and through auxiliary contact 33 to ground. Assuming that the distributor is at rest, the auxiliary contact and armatures 33 and 32 would be closed to ground as previously described. The free side of the upper winding of relay 35 is connected to battery 49. The polarization of this upper winding is such as to aid a bias spring M holding the armature of relay 36 in an open or right-hand position. When the transmitter is started through the closing switch arm 2li and Letters character is sent, the sensing armatures such as 8 will all make with the respective upper contacts l and thence to ground. The five leads from the various armatures as 8 connect not only to the respective outer distributor ring segments l through E as previously described, but also through resistances s2-a, z2-b, l2-c, Z-d and li2-e to a common line connected to the lower winding of relay 35, the latter having the other terminal of its winding connected to ground. Thus, it may be seen that reception of the Letters character will place ground on either side of the lower winding of relay 36. When any character other than Letters is received by the transmitter, at least one of the armatures corresponding to 3 will be connected to the respective lower contacts corresponding to 9 and therefore to battery 22-b. This follows inasmuch as Letters is the one character represented by five simultaneous perforations and any other character will cause one of the armatures to be connected to battery instead of ground. Thus,

current will iiow through those of the armatures 8 that are sensing no perforations, through the associated resistances `i2 and to the lower winding of relay 36, closing relay 3s to its left-hand contact.

The operation of relay 35 upon the reception of a character other than Letters will close a path through the armature and contact of relay 3s, putting ground upon one end of the winding of relay 3Q, the other end of the winding being connected to battery. Thus, the actuation of relay 3S operates relay Si?. Relay 30 will lock operated, by virtue of ground presented to its winding through its inner right-hand contact and armature, thence through the closed left-hand contact and armature of relay 2s to ground. Among the functions achieved by operation and locking relay Ziinclude: placing ground on one side of lamp 43 known as the Message Ready lamp, through the inner left-hand contact and armature of relay 3s to ground; operating the tape feed withhold magnet 29 through the outer right-hand contact and armature to ground, placing ground on the tape feed withhold magnet 29, otherwise connected to battery, as described; and in addition, relay 3l will be operated as battery connects to one side of the Winding of relay 3l, the free side connecting to the outer left-hand contact of relay 39 to ground when 30 is operated.

Relay 3l will remain operated as long as relay 3i) is operated. Operation of relay 3l interrupts the current in the winding of relay 25, allowing it to release. The release of relay 25 removes ground from the start magnet 2i as indicated in the Transmitter description and the distributor will stop rotating. Y

To summarize, the operation oi relay 3s will prevent the feeding of tape to the transmitter as previously described through operation of the tape feed withhold magnet 29, and the subsequent release of relay 25 will stop the rotation or" the distributor. This is the normal condition when a message is ready and the operator is to select the appropriate sub-receiving station to which the message is destined. The operator will receive notiiicaticn that a message is to be trans mitted by the lighting of lamp e3, one terminal of which is connected to ground through relay 3i) as previously described, and the other Vterminal of which is connected through the outer left-hand back contact and armature of relay dfi in Fig, 3, to battery, illuminating lamp 43. Notified, the operator will examine the tape being produced by the reperforator. Although the distributor has stopped rotation, and the tape feed withhold magnet 29 is operated, the reperforator Will continue to perforate in the tape the message, including the destination thereof.

Message transmission and distribution The operator has been informed by the rnessage tape of the identity of the sub-receiving station to receive the incoming message. Each of the remotely located sub-receiving stations is connected to a particular outgoing loop. .Arrangements must be made to connect any one of the outgoing loops to any one of the incoming levels. This will be accomplished by a seize relay which is located in an appropriate position with respect to the outgoing loop and the incoming levels, and each outgoing loop must have a seize relay associated with each level to which it is to be connected. With each of the seize relays, there willv be associated a preempt acc-6,199;

relay and an operating; key, whose generalfunctions Were described in the simplified diagram, Fig. l. Assuming that the prior description of thestart of a message appertains to incoming level l indicated in Figs. Band Li, the message ready lanip @Sin Fig. 2 will have been illuminated. For descriptive purposes, it may be assumed that the operator has determined that the message is addressed to the sub-receiving station connected to outgoing loop i. The appropriate seize and. preempt relays and operating keys associ.- atedV both with outgoing loop l and incoming level! are shown in the upper left-hand corner of Fig. 4. Thus, the operator will momentarily operate key de. Operation of key 4t will, cornplete the'circuit of preempt relay d? shownin Fig. 4. Operating current is supplied to the Windm ing of relay 4l from battery on one side, through operated key di?, the cuter right-hand contact and armature o' unoperated relay @d in Fig. 3, toground.

Operation of preempt relay lil produces a group of-,simultaneous occurrences. When key flopenates relay lll, theground path previously described from the outer right-hand contact of relay 44 extends not only through the left-hand armature andcontact of key et to the coil of relay ill', but inaddition, through the left-hand contacts armature ofA key lli to the No. 3 armature of relay lil'. When relayl? operates, its No. 3 armature: closes against its associated Contact and provides ground to the winding of relay itt, connected onitsopposite terminal to a battery, causing relay M to operate. The operations effected by relay. le Will be fully described at a later point. Inthe; meantime, the No. It armature of relay il has.v provided a-locking path for relay lll. This lockingpathexists at first through the armature and contacts of relay titel), the closed makebefore-break contacts of relay den to ground, When both relays l5-ct and i5-b are non-operw ated* Operation of relay it will operate relay l5- through the now closed outer right-hand armature and contact, putting ground on the Winding of relay l5-b connected on its opposite terminal to battery. The continuity oi ground provided to No. @l contact of, relay Il?, locking relaylll, will remain uninterrupted upon operation of relay --c because the inner right-hand armature and contact of 4.5c will connect ground to armature No. 1i of .relay 3'! before breaking the ground connection through the contact and armature. of tti-b and the inake-before-break con.- tact or" relay Qi-tt to armature i or relay dl. Operation of relay i5-a will in turn complete4 the circuitV of the winding of relay i5-b, through its outer right-hand contact and armature connected to ground and to one terminal of the Winding oi relay dii-l2, the other terminal of which is connected tov the battery. As indicated previously,r however, the operation o3? relay @5i-b has no ei'ect as the conductor connected to the armature of l5-b has already been connectedto groundthrough. the inner right-hand contact ol"l relay iea.

Relay M is operated and locked when key is operated, as previously indicated. This is achieved throughground connected to the outer rightehand armature and Contact of relay it in Fig. 3, to the left-hand contact and armature of operating key llt, to the armature and contact 310i relay el, tothe Winding of relay le which has its other terminal connected to a battery. During the moin-ent of time the operating key i6 is, closed, ground will be held on the Winding of relay lll! through'the previously described lock circuit ofNo. d Contact of relay 47, to the No.

armature and contact of relay All, to the righthand armature andcontact of key tti, to the leithand armature and contactar key te, to the No. 3 armature and contact of relay t?, and to the Winding of relay 44 asV previously described. A locking pathY is provided for relay le from ground to Noni armature and contact of relay ril, to the closedcontact and armature of` relay lli of Fig. 2, to the inner left-hand contactv ofv relay dit, locked` closed, to the winding or relay 44,. which has its other terminal connected tov battery.. Operation-of relay l/lor release of relay il will therefore unlock relay dill.-

Returning to the effect of the operation of relay d?, it hasbeenseen that relay ld is operatedl of contact 5 provides afpath frornground to the.

No. l armature and contact otrelay. i9 through the closed No. i arniaturerand contact of relay t9 to the closed-No. sfr-contact andarrnature of relay 6l now operated, to one terminal ofv relay 5d, shown on Fig. 3, which has, its other terminal connected to battery.1 Itr Willlater beshown that relay 58 establishes that part of the preparatory condition operating the stepping vpulse circuits.

The seize relaylzey has two energizing windings. The left-hand Winding is connectedl to the No. e armatureV and4 Contacty ofv relay t? and thence in series WithV and through its own No. i ina-kebefore-break contact and to ground through a series connection ofK each ofv the No.l imakebefore-breaklcontactsof all the seize relays. cor-k respondingv toI relay 4e in loop l, indicated, for example, as iov-ct, tothemake-before-hreak.contact onV the inner.- right-hand contact of relay 5l and to ground. Thus, only if no seize relay is operated in loop;y i, will ground be established on one side'of the left-hand Winding or seizeV relay lle-when relay lil operates. The free-side of the left-hand winding of relay tev connects to the inner right-hand contact of armature llt. Assuming that relay lllis operated and locked, the inner rightehand' contact and armature-connects to the armatureand'contact of relay 52-11.. It-Will beseen` that relay 5ft-a intermittently provides a path to battery for the left-hand Winding ofrelay le in accordance with a predetermined arrangement offeringy such, al battery connectionmomentarily to each ofv the incoming levels4 in sequence.. It may be assumed, for the purpose of discussion, that battery isfmomentarily provided to;therinnerxrightehand armature and contact offoperated relay dit, and thence tothe free left-hand winding of relay de.' Provided thatl no other seize relay is operated in loop l, relay t9' will operateif encor-the other seize relays cor'- responding to relay@ inloop;v l should" be op erated, the operatedrrelayvvill-haye an open No. limake-.before-break contact. as at lla-a; a busy condition -offloop lresults; and'seize relay; titlwill not operate. Assuming now. that; loop l, is, not otherwise busy, the seizeirelayilg Willllock through its right-hand' Winding asi follows: therightehand winding is connected to battery Von'y one side: The

acvaie'c free side of the right-hand winding is connected to No. 'l armature and contact of relay 4l, now operated. No. l contact of relay 4l in turn passes back to No. 4 armature and contact of relay it and passes thence to ground, through the No. fi make-before-break contacts of the relays corresponding to t9-a in loop i. Assuming that relay 4S has at least momentarily operated, passage of current through relay 4l, contact No. 'i and relay 49, contact No. 4 will lock relay 49 in a closed position.

It has been seen that operation of relay 4l, the preempt relay, will operate and lock the seize relay 49 if no other seize relay in the chosen loop is operative. Operation of the seize relay 9 procures other results.

Operation of the seize relay provides a ground circuit through armature and contact l of relay 49, the seize relay, to one side of lamp 54%, which will be illuminated, being otherwise connected to the battery. This lamp indicates to the operator that the incoming message is being properly retransmitted to the selected outgoing loop. Further, closing of the No. 2 armature and Contact of relay 49 provides a ground path through the center left-hand armature and contact of relay 44, now operated, to one terminal of the Winding of relay 55 in Fig. 3, which has its other terminal connected to battery.

Relay 55 provides a battery path through its armature and contact to relay 2'5 in Fig. 2, previously mentioned. Operation of relay 25, in turn, unlocks relay 35 by removing the ground from the inner right-hand contact and armature previously locking relay 3i), and the left-hand armature will now make to its associated contact providing a lock path to the right-hand armature and contact of relay 31. In addition, a ground path is provided through the right-hand armature and contact of relay 31. In addition, a ground path is provided through the right-hand armature and contact of relay 25 to the stop lever arm and contact 24, through the armature and contact of relay 23 in a path previously described to the start magnet 2|, ultimately releasing the distributor shaft i3, and allowing the distributor to rotate; the message will now proceed.

In the foregoing, it has been noted that operation of the seize relay 49 unlocks relay 30. Unlocking of relay 3l) will extinguish the Message Ready lamp 43 by removing the ground from one side of the lamp. The tape feed withhold magnet 29 will also be released by removing the ground path previously described through the outer right-hand contact of relay 36. Thus, the transmitter will be started and the tape will feed. The most important operation performed by seize relay 49, however, is to connect the transmitter output signal to the appropriate outgoing loop. The output of the distributor is provided on a path originating at the inner commutator ring S of the distributor shown in Fig. 2. The signals pass over conductor 38 in Fig. 2, to the upper Winding of relay 55. The signal will be impressed on the upper winding of relay 56 and cause it to operate in accordance with the marking and spacing pulses by passing the armature from the left-hand contact to the right-hand contact in the transition from mark to space. The lower winding of relay 56 is a bias Winding, permitting adjustment of relay sensitivity. This bias winding tends of hold relay 55 in a spacing or right- Y hand condition, and will be overcome by Ythe marking signals sent by the distributor. A marking condition causes relay 56 to stay on the lefthand contact, placing battery on lead 51. i

to the right-hand contact with the bias Winding alone energized, and places ground on lead 5l."

Thus, lead 5'! will now transmit battery for marking and ground for spacing representative of the signal intelligence and the synchronization.

Lead 51 extends to the No. 5 contact and armature of seize relay lig. It has been stated that the operation of relay 49 connects the appropriate incoming level to the desired outgoing loop and it is this connection that is made at No. 5 contact and armature of relay 48. The signal passes from line 5l to line 58 through this contact and armature and ultimately to the upper winding of transmitting relay 59. Relay 5s has a lower bias winding tending to maintain the armature in a lefthand position. Upon reception of the spacing signal on line 58, relay 55 operates to its righthand position, opening the outgoing loop circuit. With a marking signal, the bias winding alone will be energized, closing relay 59 to the left-hand contact.

When none of the seize relays is operated, the bias winding will hold relay 59 to the left-hand or marking condition.

Busy condition-stepping pulse generation It has been seen that if any of the seize relays on a desired outgoing loop is operated, it is impossible to operate any other seize relay associated with that loop. rlhe invention provides a means whereby the message received on any incoming level will be withheld and stored until the desired y outgoing loop is free.

Let it be assumed that the operator has performed all the functions previously indicated up to the point of closing the appropriate operating key, i5 for example, thereby operating relay il as previously described, and setting up the preparatory condition. It has been seen that establishment of the preparatorycondition extinguishes the Message Ready lamp i3 and operates relay 55. In general, the operation of relay 55 sets in motion the operation of the stepping pulse circuits. It will be the duty of the stepping pulse and ring circuits to offer afconnection of each of the incoming levels to each of the outgoing loops, when a connection is desired a5 a result of establishment of the preparatory condition.

The immediate function of relay 55 upon operating as a result of the establishment of a preparatory condition is to provide a battery connection through its contact and armature to the filament of the thermionic discharge tube Ell. Refleeting upon the polarity of the system described, it Will be found that ground is assumed to be at positive potential and that battery connections arermade on the negative side to the individual circuits. One end of iilament 6l is connected in potential at a point located between the positive and negative ends of the battery depending on the relative value of resistances SZ-c and 52-22. In any event, filament 5i will be at an absolute potential level somewhere between the positive or negative potential level. The anode 63 of thermionic discharge tube 55 is connected through relay @4 to ground and therefore to the point of most positive potential. Control grid 52 will be shown to have a positive voltage thereon, allowing a flow of electrons from cathode 6i to anode 53; current will thereupon be caused to iiow in the windings of relay 65. This current is .suiiicient to operate relay S4.

Operation of relay S will provide a ground path through its armature and contact to one terminal 13B` of the Windingofrelay Eef, the other terminallof which is connected to a battery, to operate relay 65; Operation of relay e Will open the ground path provided through its outerarmatureV and Contact and the winding of relay 66' to battery. Because of the normally rnade outer contact and armature of relay t5 previously described, relay.I

the thernionic discharge tube will have appliedto it avoltagepositivewith respect to thecathode, permitting the previously described iiow of' current from the lanient to the anode. This positive voltage isy developed through resistances Gl-a and 'i-b to the positive ground. The subsequent release of relay places negative `battery Voltage upon the grid through the contact and armature of relayl Until the release of relay 65, negative battery cannot reach the grid, being blocked by condenser''i. When the grid 62 becomes negative, the'floiv of current from the dlament to the anode will cease or vbecome materially reduced. This elimination or reduction of currentfiowing from the. larnent to the anode will allow relay to release,in turn releasing relay 65. This will reenergize rela-y 55, restoring the positive voltage to the grid i2 of the therniionic discharge tube, and. again allowing anode current to flow. The larnent to anode current of the therinonic discharge tube will be alternately permitted and suppressed; the associated relays Se, E5 and 36 Willrepetitively operate and release depending principally on the time lapse interposed by the slow release of the armature of relay Sii. The combination of elements comprising tube tt. and relays M, S5 and d isa form of oscillator. It has been found desirable for the purpose of this invention to adjust the` release time of the slow release relay to produce oscillations of the order oi` sixty per minute of the iilament to anode current.

The inner armature of relay 65 will also be oper ated and released upon the operation of relay t5 and will therefore connect ground tofirst the lefthand Contact and then the right-hand'contact as.- sociated with the inner armature. It is this. reversal from one contact to another Which providesy the stepping pulse desired. It. can be seen that this stepping` pulse has a rate/controlled by the interruption frequency of the therrnionic. dis-- charge tube in. the manner previously described. In net, the operation of the preempt relay 4l and consequent establishnient of the preparatory condition provides, inter-alia, the stepping pulses` to be found at the inner contact of relay S5.

Busy condition-relay ring A ring of'. relays is indicated inV Fig.r 3. These relays are shown as composed of ring gate relays 522e, 5'2--73 and 5.2.-c foreach incoming level, and associated ring control relays 53-c, andr Sal-c. Corresponding ring gate relays and ring control.y relays will be required for each in,- coming: level.

Assuming that the system is Ibeing operated for the first time, the ring will first'beenergizedas follows: upon the iirst operationoi relay 65;, av ground path is provided on. the innen armature and the made contact of relay G5. This ground l hand winding of seizerelayr 49pm Fig; i which E4 pathL continues.y from the .aforexrl@ritienecl contact tonthe made'. outer.` leftehand* armature and con.-

tactfof noneoperated.relay- 5135-0, andto the, madeouter leftehand contactf oir non-operated relay- Eel-l),V andiiinallyf to; thexmade. outer left-hand contactz'of; non-operated relay Et-a. The outer left-hand-:contactxof relay-'53% provides a ground tottheeleft-fhand.-Winding or" relay B21-a. otherwise connecteditobatterm. This-will causerelay 52-a tooperate; asenergizatorr ofeither Winding of relay: SEL-a: will foperatef it.

Relay 52H1.. Will: lock. through'` itsvv inner right.- hand'v contactandarmatunerto, the outer righthand contactand armatureiof relay 5Zb,made

'- when 5241 isireleased-,.togzground, This will providel aground connection on one terminal of the rightnandi; winding: of; relay {iz-a, the; other terminal' of whichdszconnectedto the bath-sry,v

looking 52?-a closed'. irrespective of relay, 53am. A- primary'object in.: operating relay EZ-d is.to close itsv lette-hand make contacts. handarniature andL-contact-connects through the madellett-hand contacts.. andarmatures of relays F12-band52c to.z-battery,xproviding a battery; tothe innel` right-hand armature and contact: ot relay 4A whichmay. belocked: operated asstatediin theprevious description. If relay lillV operated, battery potential. travels from the inner right-hand contact ofi relay 44 to the leithas itsopposite terminaloonnected through the closed No.A Si contactfof.' the preempty relay No.

4'. through the path previously1 described. The

seizerelayS-will operate in, accordance with the priordeseription; or its, operation,I provided no other seize relayzin'; that; outgoing loop is operated'. if line dii-l1 has; an open. make-beforereak contaot',..located..` in one ofthe relays cor-- responding to.- Ait-f1..y or.` 5.1!, seize relay te cannot' operate; a moment. of'.` time later the stepping Itv can.-

a connection. fronr level. l to all of theoutgo-Y ing' loops; a. batteryv connection is madeI to thev left-handA Winding. of eaohof' the seize relays.

If the associated preempt relay of any oi` these seize'relays isA operated, a-v connection will be attempted,y dependent. on Whether another seize relayA in the same-outgoingl loop is operated.

Assuming-thatthe desired outgoing loop-indicatesa busy condition, the relay E5 Will release after a predeterminedv period of time dependent upon the stepping pulsel period, and its inner left-hand: armature Will return to the released position; Thereupon, ground Willbe provided to the center right-hand armature and contact of relay 52-a now in a closedzposition through the of relay 52.a;but relay d2-a is-still locked by its right-hand winding.

After a period of time, relay 65 again operates Thisv left.-k

and now a new ground path will be provided through the inner left-hand armature and front contact of relay t5 in the operated condition to the now made inner left-hand armature and contact of relay .t3-a to the left-hand winding ci relay E32-Z9 which has its other terminal connected to battery. Relay 52-h will operate.

Operation of relay Sii-b will break the lock path at the outer right-hand armature and contact of relay {i2-b to relay 52-a and allow -a to release; no current now iiows through either winding of relay EE-a. Relay 52-b locks through its righthand winding to its inner right-hand contact and armature and through the outer right-hand contact and armature to ground of relay 5'2-0 in the manner described for relay 52-a. The battery potential ofered to the left-hand portions of the seize relays on incoming level l is broken by the release of relay iii-a and the battery is now supplied to the corresponding seize relays of the second incoming level. This occurs through the closing of the left-hand contact and armature of relay 52E-b, the remaining path through the second level being identical with that as described for the first level. Similarly, the operation of relay EE-b operates relay 53-17 by applying a ground to its winding and, in turn, relay .E3-b locks through its inner right-hand contact and armature through the outer right-hand contact and armature of relay 53-c to ground. The locking of relay .S3-b will now unlock relay 53-a through the opening of the outer right-hand contact of re1ay 53-b.

To summarize, each of the ring gate relays 52-a, 52-b and iii-c will be successively operated dependent upon the movement of the inner left-hand armature oi relay 65 and a battery potential will be offered to the left-hand windings of the seize relays on the several incoming levels in sequence. The operation of relay eZ-a follows the release of relay 52-c and the relay ring will continue through its repetitive cycle. In effect, this will offer an operating connection from each of the incoming levels to all of the outgoing loops successively for the levels. When a particular seize relay associated with the appropriate incoming level and outgoing loop finds its associated preempt relay in operated condition, that seize relays will operate if the line is not busy.

it is welltc recall that the stepping pulses occur as a result oi the operation of relay 5t, and that relay 5&3 operates solely when one of the preempt relays has been operated by operation of the appropriate operating key. Thus, when all incoming calls have been satisfied and on preparatory condition is to be found at any level, relay Si! will release; the stepping pulses Will cease and the relay ring will remain in the position in which it was at the time relay 5@ released until a preparatory condition is reestablished.

Additional incoming levels will require additional ring gate and ring control relays similar to relays Eil-a. and :i3-o, but operation would be otherwise similar.

Termination of message t has been stated that one object of the invention is to provide means whereby the equipment set in motion through the reception of the message will be arrested upon the termination of a message. The following describes the means whereby the central receiving apparatus is stopped upon a reception of a certain predetermined code grouping.

' When the sensing pins connected to the sensing armatures 8 receive a given character, the initial step in the termination arrangements may be made. For example, for the character controlling the movement of the receiver printing platen to upper case, known in the art as Figs., the sensing armatures may have spacing and marl:- ing on their respective contacts in accordance with the following: l/IMSMM, where M is mark and S is space Analyzing the eects of such a combination upon the various armatures `8, in Fig. 2, it will be noted that a mark condition would exist on the iirst and second armatures, a space condition on the third armature, and a mark condition in the fourth and fifth armatures looking downward. The iii-st, second, fourth and fifth armatures would therefore be connected to ground; the third armature would be connected to the battery. Leads running from the iirst,

second, fourth and fiith sensing armatures 8 will connect to resistances SQ-e, it-d, Sil-b and {iS-o respectively. The other ends of these resistances are connected in common to the lower winding of relay lil, and through that winding to battery. The third of the sensing armatures would 'oe connected through the appropriate lead to resistance ESE-c and to the upper winding of relay It and thence to ground. Thus, a voltage will exist across both the upper and lower windings of relay it when the iive sensing armatures a are sensing the character representing Figs No combination other than Figs will provide sufficient current to operate relay 76; Yrelay 'l is adjusted so that the core flux density resulting from current through the upper and lower windings combined as previously described will overcome the bias spring il, thus operating only upon the receipt ci the Figs character. Operation of relay 'i will provide a path from ground to the now closed armature and contact of relay lil to the right-hand winding of relay 34 through whichA the path extends to battery; relay 34 will now operate.

Relay 3d will lock through its left-hand winding, contact and armature through the auxiliary contact and armatures 32 and 33 to ground; the auxiliary contacts are closed provided the distributor is stopped. In addition, operation of relay 3i will provide a ground path through its right-hand armature and contact to the righthand winding of relay 'i6 through which the path extends to battery; relay 'iii will then operate.

Relay 'i6 has a slow release characteristic; a short-circuit is provided between its inner contact and armature and its left-hand winding. Thus, the opening of the auxiliary contacts 32 and 313 and the subsequent unlocking of relay 34 will not immediately release relay l5, at least until the next character is received.

If the next character received is H, the sensing pins will convey to the sensing armatures 8 to the code group represented as SSMSM where M is mark and S is space as before. The code grouping for the H will connect the rst, second and fourth sensing armatures to battery, and respectively to resistances 'S8-e, {S8-d and t3-b. Each of these resistances is in turn connected in common to the terminal of the lower winding of relay 'il which has its other terminal connected to ground. Similarly, the third and fifth sensing armatures are connected from ground to resistances ts-c and B-a; and thence in common to the upper winding or" relay 'l2 which has a connection to battery. As in the case of relay '10, relay 12 will have a maximum current said transmitters supplied with said occasionalP` intelligence, an oscillator activated by any ci the said preempting means, pulsing means responsive to the alternating output of the said oscillator, individual connecting relay means coupled to each of said preempting means and controlled by the said pulsing means to seize said preempted loops for association with said transmitters, and means common to all of said transmitters for distributing the pulses of the said pulsing means sequentially to said connect ing relays in groups corresponding to the indi vidual levels oi the said transmitters and simultaneously to all the connecting relays of the group.

5. In a telegraph switching system, a plurality of incoming levels having intelligence thereon, an equal plurality of transmitters, each associated with one of the said incoming levels, means to supply said intelligence to the said transmitters, a plurality or outgoing loops a plurality of preempting relays in groups individual to each incoming level, each of said groups having a preempting relay individual to each outgoing loop for preempting said loops for se lective connection to any one of thesaid transmitters supplied with said intelligence, a seizing relay individual to each of the said preempting relays and controlled in part by the said preempting relay, said seizing relays selectively coupling the transmitters to the outgoing loops, a pulse oscillator activated by any of the preempting relays, a relay ring having a plurality of steps equal tothe number of incoming levels, each of the steps of the said relay ring including relay means coupled in common with the said seize relays in groups individual to each incoming level to control in part the said seize relays, and means for sequentially and repetitively energizing the steps of the said relay ring from the pulses of the said pulse oscillator.

6. In a telegraph switching system according to claim 5, wherein the pulse oscillator comprises a thermionic discharge tube having a cathode, grid and anode, a relay coupled in the anode-cathode circuit of the said thermionic discharge tube, means to energize Athe anodecathode circuit or the said thermionic discharge tube, and means to interrupt the said anodecathode current a given period of time after the latter current has reached a predetermined magnitude. f

7. In a telegraph switching system according to claim 5, wherein the steps of the said relay ring comprise each a gate relay and a control relay, means to control in part the said seizing relays in accordance with the said gate relays and in groups individual to each incoming level corresponding to the steps of the said relay ring, means to interconnect the control relays of the said relay ring in sequential response to the pulses of the said pulse oscillator, and. means to control the said gate lrelays in accordance with the said control relays.

l8. In a telegraph switching system according to claim 5, wherein the said means to supply the 2o said intelligence from the said incoming line to the transmitter comprises reperforation means to derive a tape having perforations in accordance with the said intelligence, and perforation sensing means responsive to the perforations of the said derived tape to provide discrete electrical impulses from the said perforations, thereof.V

9. A selective telegram switching system for retransmission of message material from individual incoming levels to individual outgoing loops comprising seizing relay means in common with each of the incoming levels and outgoing loops, manually operable preempting means to register each of the said seizing relay means for establishing of a connection between the said incoming levels and outgoingA loops, a relay ring having steps associated with the said incoming levels, each of'said steps having a gate relay in series with the said preempting means to control the said seizing relays in groups conn mon to the said incoming levels, means to generate stepping impulses, said latter niea-nsac'tivated by each of the said preempting means for sequential distribution of the said stepping irnpulses to the gate relays of the said relay ring, and busy guard means deenergizing all of the said seizing relays in the group common to the busy outgoing loop excepting the rst operated seizing relay means.

10. In a selective telegraph switching system according to claim 9, the circuit comprising iirst relay means responsive to a iirst predetermined code contained in the said message material to delay transmission of the said message material until the operation of the said preempting means and second relay means responsive to a second predetermined code contained in the said mes` sage material to terminate transmission of the said message material and to restore the said preempting means to a non-operated condition.

l1. A selective telegraph switching system for retransmission of message material from individual incoming levels to individual outgoing loops comprising seizing relay means in common with each of the incoming levels and outgoing loops, manually operable preempting means to register each of the said seizing relay means for establishment of a connection between the said incoming levels and outgoing loops, a relaylring having steps associated with the said incoming levels, each of said steps having a gate relay in Series with the said preempting means to control the said seizing relays in groups common to the said incoming levels, means to generate stepping impulses, said latter means activated by each of the said preempting means for sequential distribution of the said stepping inipulses to the gate relays of the said relay ring, busy guard means deenergizingalloi the said seizing relays in the group common to the busy outgoing loop excepting the first operated seizing relay means, and means responsive to the said preempting means to delay transmission of the said message material common to the said deenergized seizing relays. ,I I

l2. In a telegraph switching system for re transmitting material including a trai receiving,r station having a plurality ci. coming lines and a plurality of outgoing loops, plurality of sub-receiving stations each associated with the Vsaid outgoing loops, a circuit comprisingl first relay vmeans having' discrete segments coupling eachgof the said incoming lines and out-- gong loops in common, manually operable -second relay means for selectively designating individual segments of the said rst relay means for energization, third relay means associated with the segments of the said first relay means in ranks common to each of the said incoming lines, said third relay means energizing the segments of the said rst relay means in groups according to the said ranks, an oscillator having a pulsed output, and means to interconnect the ranks of the said third relay means in successive and repetitive operational sequence responsive to the pulsed output of the said oscillator.

13. In a retransmitting telegraph switching system including a central receiving station having a plurality of incoming lines with message material thereon and a plurality of outgoing loops, a plurality of sub-receiving stations coupled to the said outgoing loops, the circuit comprising, discrete connecting relays coupled in common With each of the said incoming lines and outgoing loops, a plurality of preempting relays each associated with one of the said connecting relays designating individual connecting relays to couple the said incoming lines and outgoing loops selectively, manually operable keys for energizing the said preempting relays, a plurality of gate relays associated with the said connecting relays in ranks common to each of the said incoming lines, said gate relays energizing the said connecting relays in groups according to the said ranks, an oscillator energized by any ofthe said preempting relays and having a pulsed output, and means to energize the said gate relays in a closed operational ring having progressive steps responsive to the said oscillator.

14. In a telegraph switching system, a plurality of incoming levels having intelligence thereon, an equal plurality of transmitters, each associated with one of said incoming levels, means to supply said intelligence to the said transmitters, a pluralty of outgoing loops, a plurality of preempting relays in groups individual to each incoming level, each of said groups having a preempting relay individual to each outgoing loop for preempting said loops for selective connection to any one of the said transmitters supplied with said intelligence, a seizing relay individual to each of the said preempting relays and controlled in part by the said preempting relays, said seizing relays selectively coupling the transmitters to the outgoing loops, a source of pulses activated by any one of the said preempting relays, a relay ring having a plurality of steps equal to the number of incoming levels, each of the steps oi the said relay ring including relay means coupled in com mon with the said seizing relays in groups indi vidual to each incoming level to control in part the said seizing relays, and means for sequentially and repetitively energizing the steps of the said relay ring from said source of pulses.

15. In a telegraph switching system, a plurality or incoming levels having intelligence thereon, an equal plurality of transmitters each associated with one of said incoming levels, means to supply said intelligence to the said transmitters, a plu rality of outgoing loops, a plurality of preempting relays in groups individual to each incoming level, each of said groups having a preempting relay individual to each outgoing loop for preempting said loops for selective connection to any one of the said transmitters supplied with said intelligence, a seizing relay individual to each of the said preempting relays and controlled in part by the said preempting relays, said seizing relays selectively coupling the transmitters to the outgoing loops, a source of pulses activated by any of said preempting relays, a commutating circuit having a plurality of steps equal to the number of incoming levels, each of said steps including means coupled in common with the said seizing relays in groups individual to each incoming level to control in part the said seizing relays, and means for sequentially and repetitively energizing the steps of said commutating circuit from the pulses generated by said source of pulses.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,749,444 Rae Mar. 4, 1930 2,410,540 Wight et al Nov. 5, 1946 2,546,627 Blauton Mar. 27, 1951 2,546,630 Currie Mar. 27, 1951 2,632,044 Light Mar. 17, 1953 

